Field of the Invention
The invention relates to an apparatus for torque measurement on rotating torque shafts, in particular in motors having a torque shaft, in which optical response signals are generated in an axially offset manner at least at two points on the torque shaft by radiating light onto the rotating torque shaft, an azimuthal offset over and above a rotary movement is determined for evaluating the signals, and at least one light source and an associated device for generating and evaluating the response signals are provided.
In practice, it is required to detect the torque output by machines. With electric machines, it should be possible to perform the measurement, in particular, inside the motor housing. However, it is also necessary to be able to determine the torque accurately in the case of the use of machines in industrial plants, for example electric motors for driving rolling mills, with the aim there being to perform the measurement outside the motor.
The torque of rotating machines is frequently measured by torque measuring shafts which are mounted between the motor and the driven machine. In that case, the torque measuring shaft includes a spindle, the torsion of which is detected through a strain gauge, for example. The signal transmission is performed in that case through sliprings or telemetric methods.
It has already been proposed to determine the torque through micromechanically produced capacitors which are fitted on the torque shaft and have a capacitance that is varied by the torsion. However, that also requires telemetric signal transmission. In addition, it is also possible to use configurations with surface wave filters for torsion measurement, which is described, for example, in German Published, Non-Prosecuted Patent Application DE 195 32 601 A1.
Furthermore, German Patent DE 44 28 362 C2 proposes a method for contactless detection of the movement, in particular the rotary movement, of a machine part. To be specific, a pulsed light beam is directed onto a measuring point at which markings having a defined length that are disposed on the machine part sequentially in the direction of movement thereof pass by, and light reflected by the markings is detected and evaluated. That method develops a method previously known from UK Patent Application GB 2 093 991 A in such a way that the light beam is pulsed at a prescribed frequency and focused in such a way that upon striking the markings it generates a sequence of light points which can be counted in a simple way. It is also possible in that case to measure torque through the use of a twofold, axially offset measurement. The pulsed light beam is advantageously generated by a laser. In addition, UK Patent Application GB 2 093 992 A likewise discloses a method which operates with pulsed lasers and in which irradiation is performed in an axially offset manner at two points on the rotating shaft and the torque is determined by defining a temporal reference point for the axial offset of the response signals. That method has proved not to be functional in practice.
U.S. Pat. No. 2,586,540 discloses a torsion meter in which the shaft is optically scanned. However, German Published, Non-Prosecuted Patent Application 30 11 700 discloses an apparatus for load-dependent measurement of the torque of a torque shaft in which the torque shaft is irradiated with light in an axially offset manner and subareas which reflect radiation supply torque-dependent response signals with the twisting of the torque shaft.
In addition, German Published, Non-Prosecuted Patent Application DE 195 23 756 A1 discloses a sensor which detects the force or the torque on a working machine. The sensor is constructed as an optoelectric sensor that generates at least one light path in the case of which the quantity of light transmitted through the light path, or the magnitude and variation thereof, are a function of the force of the torque on the machine.